Why the wide prong on a plug?

A lot of holiday lights (particularly miniature and LED) have
non-polarized plugs. Also, some "wall warts", including the one that
came with my new bluetooth headset. The use of a non-polarized plug on
these things makes it more versatile.

The UK did redesign its plug and socket )and wiring system) during the
war and postwar years to the now current 3-pin, fused 13A type. At
that time, of course, there were far fewer electrical appliances in
use, and a massive post-war housebuilding programme.
The postwar system uses unlimited numbers of 13A sockets (outlets) for
general use within a limited floor area, wired on a ring and protected
by a 30A fuse or 32A circuit breaker. This saved copper and allowed
more flexibility than having a small number of sockets per fuse. It
was considered unsafe to allow appliance flexes to be connected to
such a high rated circuit with no further protection, and the plug/
socket combination had to provide the fuse. It was decided to place
the fuse in the plug, and to use a new plug configuration so that
older unfused plugs could not be used.
Fixed space and water heaters must be supplied by individual circuits,
and good practice now is to provide a separate circuit for the kitchen
which now has a large number of high load appliances unforseen in
1942.
See
http://en.wikipedia.org/wiki/BS_1363
Owain

One thing I really liked about the UK system was the availability of
plugs with integral switches, so that appliances without a built-in
switch could still be turned off without pulling the plug.
And, IIRC, separate circuits for lighting and sockets.
Perce

However, I couldn't find any of those the last time I was there -- 8
years ago.

Forgot to mention that the plug-mounted fuses came in a range of current
ratings: 2A, 5A, 7A, 10A and 13A, IIRC. I think the plugs normally came
with a 13A fuse, but one was supposed to install a fuse appropriate to
the appliance to which it was to be connected.
Perce

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